Coaxial cable connectors that require crimping are associated with certain disadvantages. Crimping tools tend to wear out with repeated use, and crimping does not provide a satisfactory seal. A number of crimpless connectors have been developed which attempt to overcome these problems.
One type of crimpless connector receives a compression sleeve, which is first broken away from a plastic ring mounted on the connector, and then slid over the cable and finally inserted into the annular cavity between the inner wall of the connector and the jacket of the cable. A tool is used to push the compression sleeve fully into the connector with a snap engagement.
A problem with this connector is that it can be awkward to break the compression sleeve away from the connector and then thread it onto the cable, particularly when used in field installations where there may be adverse weather conditions. The compression sleeve can as well be inadvertently threaded onto the cable backwards, and it can also be dropped and lost.
An alternative crimpless connector has more recently been provided, which permits the cable to be secured to it simply by pushing the cable into the connector and subsequently pulling it back. The body of this "push-pull" connector has a bushing mounted within it near the cable receiving end having a diameter to closely receive the cable. The body of the connector also has within it an annular mandril having a bore to receive the stripped core of the cable, and having a sleeve adapted to engage the cable beneath the jacket by pushing the cable and the mandril together. This stretches the jacket of the cable to a diameter greater than the internal diameter of the bushing.
The mandril is moveable from a position in which the sleeve is surrounded by the bushing in which the sleeve may be engaged to the cable, to a position in which the sleeve is at least partially within the bushing in which the jacket is frictionally engaged by the bushing by pulling the cable away from the connector after it has been pushed onto the mandril sleeve.
While the push-pull cable connector has many advantages, it does not lend itself to all applications. In some publicly accessible installations, for example, it is the usual practice to cover the threaded posts to which the cables are connected by a security ring, making the threaded portion of an installed cable connector inaccessible to finger manipulation or common wrenches or pliers. Unauthorized removal of the cable is thereby discouraged as a special tool is needed to fit within the security ring.
Due to the close tolerances of the standard security ring, the dimensional limitations of the push-pull connector present a significant obstacle. The internal bushing and mandril of the push-pull connector require a larger body diameter than can be accommodated in the standard sized security ring. While a larger security ring could be substituted, doing so would present additional costs.
It has also been found that the push-pull connector can be awkward to use with coaxial cable having multiple layers of braided shielding. Because of the limited travel of the mandril and bushing, the inserted cable must be trimmed to expose only a short distance of braided shielding. Folding back one layer of braided shielding presents little difficulty. However, manipulating multiple layers of braided shielding that are as short as required can be awkward. While a push-pull connector could be made with a longer travel for the mandril and bushing, thus allowing a longer trimmed section for the cable, this would require a longer overall connector length which would increase material costs.